1. Field of the Invention
The present invention relates to an optical interconnection structure, and more particularly, to a structure of optical interconnection between an optoelectric device and a single mode optical fiber, for enlarging alignment tolerance.
2. Description of the Related Art
In an optoelectric device module, light transmission must be accomplished between smaller devices compared with existing electric elements. Thus, the efficiency of optical coupling between an optical source, such as a laser, and an optical fiber or optical waveguide becomes important to show the optimal performance of the optoelectric device module. The optomechanical characteristics for optimizing this optical coupling efficiency and time-consuming stabilization of thermo-mechanical characteristics are essential in determining a design, a manufacturing method, and the price of a product. Up to now, in optical connection between a single mode optical fiber and a laser diode, an edge-emitting diode laser has usually been used as the optical source. However, the edge-emitting diode laser has a laser gain medium with a thin thickness, producing an asymmetrical beam due to astigmatism, so that integration with a single mode optical fiber requires a high level of technique and a high cost. In practice, an optical fiber for single mode operation has a core diameter between 5 .mu.m and 9 .mu.m, and the accuracy of alignment necessary for keeping a connection loss within -3 dB is not exceeding 0.5 .mu.m. Up to now, many attempts have been made to reduce the costs for aligning single mode optical fibers with lasers, as follows: (1) semi-automatic or automatic active alignment; (2) semi-automatic passive alignment; (3) solder reflow passive self-alignment; and (4) mechanical feature alignment. However, the above attempts are still restrictive successes. The alignment tolerance has been recently enlarged within +/-2 .mu.m using extended beam emission from the edge-emitting diode laser, still the above alignment methods require costs at least five times higher than those for multimode module packaging.